Caption: DNA helices. Computer artwork of many DNA double helices. A molecule of DNA (deoxyribonucleic acid) consists of two helical strands coiled around the same axis, each strand consisting of alternate phosphate and sugar groups. The strands are held together in a double helix by the hydrogen bonds formed between nucleotide bases attached to the two strands. There are four bases; adenine (A), cytosine (C), guanine (G) and thymine (T). The sequence of the bases in the molecule forms the genetic code. The genetic code provides the necessary hereditary information needed to construct highly specific proteins that determine structure, function and behaviour of all cells.